1. Field of the Invention
This invention relates to the interconnection and packaging of integrated circuits, and particularly to a module for compactly interconnecting a number of integrated circuit die in a desired manner and maintaining them under temperature-controlled conditions. The invention also provides a module containing such die which may be adapted to be connected to a printed circuit board, socket or other such connector.
2. Description of the Prior Art
The interconnection and packaging of integrated circuit die, commonly termed "chips," in a digital computer is crucial to the cost and performance of the resulting machine. As improvements in fabrication technology permit integrated circuits to have increasing numbers of components and connections per unit area, the interconnection and cooling of such circuits becomes progressively more difficult. In addition, while the extremely small size of individual transistors and other integrated circuit components permits enhanced speed of operation of an individual chip, an increasingly significant source of delay in the overall speed of operation of computers incorporating those components is the delay inherent in the transfer of signals among separate integrated circuits. Thus, to minimize propagation delays as between chips, designers of today's digital computers attempt to situate the integrated circuits making up the overall system as close together as possible. Unfortunately, as the integrated circuits are spaced increasingly closer together, the problems of interconnecting and cooling the circuits become more and more severe.
Many different approaches have been proposed and employed to interconnect and package groups of integrated circuits in digital computers. For example, a survey of this technology appears in "Microelectronic Packaging" by A. J. Blodgett, Jr., Scientific American, July 1983, pp. 86-96.
Among other technologies, Blodgett describes the thermal conduction module used by IBM in its 3081 series systems. In that module, integrated circuits are bonded face-down to a ceramic substrate upon which a pattern of electrically-conductive material has been formed. The ceramic substrate includes a sandwich of many individual layers of ceramic material, each supporting a patterned layer of electrical conductors. The various layers of electrical conductors are separated from one another by the intervening ceramic. Vias formed through the ceramic material are used to interconnect desired portions of the electrically conductive material on one layer to desired portions of the electrically conductive material on another layer. The bottom layer of the substrate is coupled to pins which mate with corresponding openings in a printed circuit board or other connector. Heat is dissipated from the integrated circuits primarily by spring-loaded metal pistons, one of which bears against the exposed back side of each circuit. In turn, the pistons are cooled by water circulating through channels in a plate attached to the piston assembly.
Another article discussing the cooling and interconnection of integrated circuits in mainframe computers is "Cooling Modern Mainframes--A Liquid Approach," by E. A. Wilson, Computer Design, May 1983, pp. 219-225. That article describes another water cooling system for cooling packages in a mainframe computer.
Prior art approaches to interconnecting and packaging multiple integrated circuits, however, suffer from several disadvantages. First, the circuits are not as densely packaged as desirable because of inefficient heat transfer between the integrated circuit and the heat exchange medium, and because the pitch of the electrical connections on the substrate cannot be as small as desired. For example, in the 3081 series module described, the thermal coupling between the spring-loaded piston and the back side of the integrated circuit is inefficient. This inefficient contact does not permit as much heat to travel from the chip into the piston as desirable. Secondly, because the conductive pattern formed on the ceramic substrate consists of screen-printed, thick film lines. The density of the lines is very low. To meet higher density line requirements, additional layers of ceramic/interconnections must be employed, thereby increasing the cost of the module and the difficulty of fabricating it.